1. Technical Field
The present invention relates to a sheet folding apparatus for folding a sheet with an image formed thereon, for example, and more particularly, to improvements in the sheet folding mechanism for enabling a sheet to be folded in a correct fold position with a simplified structure.
2. Description of the Related Art
Generally, this type of sheet folding apparatus has been known as an apparatus for folding a sheet with an image formed thereon by an image formation apparatus such as a printing press, printer apparatus and copier in a predetermined fold position to perform finish processing. For example, Japanese Patent Application Publication No. 2008-247531 proposes an apparatus which is coupled to a sheet discharge outlet of an image formation apparatus, folds a sheet with an image formed for filing, and carries the sheet out to a subsequent binding processing apparatus.
The sheet folding apparatus for thus folding a sheet in half or one-third to carry out is configured as a post-processing apparatus of the image formation apparatus, or as a unit incorporated into the image formation apparatus or binding processing apparatus. Then, as a folding form, for example, for filing, various folding forms such as ½ folding, ⅓ Z-folding and ⅓ letter-folding are known corresponding to the intended use.
Then, the folding apparatus which is coupled to or incorporated into the image formation apparatus, binding apparatus (finisher apparatus, bookbinding apparatus) or the like is comprised of a folding processing mechanism and a transport mechanism for feeding a sheet to the folding processing mechanism to set. For example, Japanese Patent Application Publication No. 2008-247531 proposes the apparatus in which a roller pair for folding a sheet bunch is provided in a collection guide for collating sequentially fed sheets in a bunch form, and a folding plate disposed in a position opposed to the roller pair with the path therebetween inserts a fold of the sheet bunch in a nip point of the roller pair.
Similarly, Japanese Patent Application Publication No. 2007-320665 and Japanese Patent Application Publication No. 2008-007297 disclose apparatuses in which a roller pair and folding plate (folding blade) are disposed in a path for feeding a sheet, and the folding plate inserts a fold position of the sheet in a nip point of the roller pair to fold. Then, the transport means for feeding the sheet front end portion and rear end portion on the upstream side and downstream side of the folding roll is comprised of a front end stopper and a belt in the apparatus described in Japanese Patent Application Publication No. 2007-320665, while being comprised of rollers in the apparatus described in Japanese Patent Application Publication No. 2008-007297.
Then, control is made so that a sheet velocity for inserting a sheet by the folding blade after once halting the sheet fed to a folding position, sheet velocity for folding the sheet by the folding roll pair, sheet velocity for feeding the sheet by the transport means on the upstream side and sheet velocity for feeding the sheet by the transport means on the downstream side are the same as one another.
As described above, when the sheet is folded in a predetermined fold, the conventional mechanism is comprised of a roller pair, and the folding blade for inserting the sheet in a nip point of the roller pair. In such a folding mechanism, control is made so that the sheet is once halted with reference to the fold position after being carried in the path, and then, is inserted in the nip portion by synchronizing the folding blade and the transport means for feeding the sheet at the same velocity. Then, the sheet front end side and rear end side are fed at the same velocity, or one of the sides is regulated in the position by a stopper or the like, while feeding the opposite side by the transport means.
Thus, conventionally, control is made so that the roll pair for folding the sheet, the blade member for pushing the fold position and the transport means for feeding the sheet end portions are synchronized with one another and given the same velocity. Therefore, for example, when the operating timing of the blade member causes timing deviation due to accuracy error, rattle or the like, the timing deviation becomes a cause of misalignment of the fold position of the sheet, or of occurrence of a wrinkle. Similarly, when friction of the transport means (rolls, etc.) for feeding the sheet changes with time, misalignment of the fold position, wrinkle and the like occur.
Further, for the sheet to fold, the transport means is provided on the downstream side of the folding position to be rotated forward and backward, is rotated forward in feeding the sheet to the folding position, and then, is rotated backward to feed the sheet in the nip position. Therefore, there are defects that the mechanism is complicated, and that concurrently therewith, the control is difficult.